Dimethacrylate-based networks were modified with well-defined organic-inorganic building blocks, i.e., polyhedral oligomeric silsesquioxanes (POSS). POSS were incorporated in the polymer networks either as dangling chains or as cross-linking points. For this purpose, the POSS functionality was varied. The influence of the structure of the organic substituent of the POSS cage was also investigated. The structure of the POSS-modified networks was determined by WAXS, TEM, and thermomechanical analysis. The POSS as a pendant unit on the network backbone shows a strong tendency toward aggregation and crystallization, depending on the nature of the organic ligands. The POSS-POSS interaction was found to be the main parameter governing the network morphology. However, dynamic mechanical properties remain nearly at the same level as the neat matrix. Multifunctional POSS shows a higher miscibility with the dimethacrylate monomer and disperses very well in the cured network. As expected, the rubbery modulus grows with increasing amounts of POSS according to the high functionality of these additional cross-links, whereas the glass transition temperature remains constant. It is also demonstrated that if the polymerization occurs at high temperature, the distribution of relaxation times is reduced and more homogeneous hybrid networks, in terms of molecular mobility, are obtained.